Patent GB-660195-A (GB)
Title: Improvements in or relating to electric control systems for fluid fuel burners
IPC: F23N5/10
Filed: 1948-08-31
Abstract: 660,195. Electrically-actuated valves. ROBERTSHAW-FULTON CONTROLS CO. Aug. 31, 1948. No. 22934/48. Addition to 601,739. Class 135. [Also in Group XI.] The safety control system for the main and pilot burners of fluid burning apparatus as described and claimed in the parent Specification is modified in that the switching means for opening and closing the circuit energizing the electromagnetic reset means for overcoming the bias tending to close electromagnetic valve means, controlling the fuel supply to at least the main burner, comprises a main switch and a delayed-action switch adapted to be mechanically operated by the manual operation of the main switch, whereby upon closing of said main switch the delayedaction switch opens said circuit to de-energize the reset means after a predetermined time delay long enough to enable flame-responsive means to energize the electromagnetic valve means sufficiently to hold the latter open. The supply of fuel through a pipe 12 to the main burner 10 is controlled by a manually operable valve 14 and an electromagnetically operated safety control valve 16, the valve 14 incorporating an electric switch which is open when the valve is closed and vice versa. On moving the handle 18 of the valve 14 to the valve open-switch closed position, an electric circuit is completed from lines 80, 94 through the contacts of a mercury switch 88, the switch in the valve 14, the primary winding 64 of a transformer 60, and a cut-out 76. The energization of the coil 64 raises against the action of a spring 67, an armature plunger 62 which in turn raises the reset rod 50 of the control valve 16 to lift the valve member 28 off its seat 25 against the action of a spring 32. Fuel is then allowed to pass through a passage leading from the valve opening 26 to a pipe 48 and thence to the pilot burner 46. A valve member 54 on the rod 50 closes the lower end of the opening 26 to cut off the supply to the main burner, although the member 54 may be omitted to allow fuel to pass also to the main burner. The fuel is ignited by a resistance coil 68 in series with the secondary winding 66 of the transformer 60. Meanwhile the movement of the handle 18 to the valve open-switch closed position has fitted the mercury switch 88 and after a predetermined time delay the circuit through the switch contacts is broken and the transformer 60 is deenergized thereby releasing the plunger 62 and de-energizing the igniter 68. The valve 16 is now maintained open by the action of an electromagnet 36 having a coil 38 energized by a thermocouple 40 heated by the pilot burner 46, the said electromagnet 36 holding an armature 34 secured to the upper end of the valve stem 30. The closure member 54 if included no longer prevents the flow of fuel to the main burner 10 and such fuel is ignited by the pilot burner to complete the starting operation. In the event of the pilot flame being extinguished, the thermocouple 40 cools and ceases to generate sufficient current to retain the armature 34 against the action of the spring 32 so that the valve 16 closes. The system is re-started by manual operation of the handle 18 to close the contacts of the switch 88 and to open the valve 14. In the event of the switch 88 failing to open after the predetermined time delay, and the igniter 68 simultaneously fails, a cut-out 76 operates to close the valve 16. An alternative system is described in which the fuel supply to the pilot burner is controlled by the valve 14 only, and the transformer 60 is replaced by an electromagnet energized by a separate transformer and controlled by a double time-delay device so that it is energized after a short period to open the control valve of the main burner, and after a further period is de-energized together with the igniter to produce the normal state of operation in which the system is controlled by the thermocouple. Specifications 624,742, [Group XI], 625,696 and U.S.A. Specification 2,276,751 are referred to.